Yersinia pestis (Yp), causative agent of plague (PL), and Mycobacterium tuberculosis (Mtb), causative agent of tuberculosis (TB), are two bacterial pathogens of importance in both global and national public health. In recent times, the threat of bioterrorism has added another dimension to the relevance of these bacteria. The Center for Disease Control and Prevention has included Yp and multiple-drug resistant Mtb in the categories A and C, respectively, of biological agents for terrorist attacks. There is a pressing need to develop new and alternative antimicrobial drugs against conventional and unconventional targets in Yp and Mtb that could be used to treat disease produced by multiple-drug resistant strains of Yp and Mtb resulting from natural emergence or bioterrorism. The long-term objectives of our research are to identify new drug targets in Yp, Mtb, and other pathogens and to develop antimicrobial inhibitors against these targets. Adequate iron homeostasis is an essential process for virulence in Yp and Mtb. The proteins of systems involved in iron acquisition in Yp and Mtb represent alternative targets for the development of new drugs that will restrict the growth of the pathogens in the human host. We propose to search for compounds that restrict the growth of Yp and Mtb by inhibiting iron acquisition functions in compound libraries. To this end and building on the PI's extensive experience and insights into the synthesis of bacterial iron chelators required for iron acquisition, we plan to utilize two independent but complementary high throughput screening programs per organism that will allow for the identification of such inhibitors in compound libraries. The first program will use cell-free assays, while the second program will use live-cell assays. Between the two programs, a total of five screens are planned: one screen based on a cell-free assay and two based on live-cell assays for Yp, and one screen based on a cell-free assay and another based on a live-cell assay for Mtb. The identified inhibitors will constitute a base for the rational development of drugs with clinical value in subsequent studies, hopefully conducted with pharmaceutical collaborators. Such drugs will be useful in the treatment of Mtb and Yp infections.